The invention relates to an apparatus for the comminution of suspended fibre material, in particular for the milling of paper fibres and/or of cellulose fibres. These apparatuses typically comprise a housing having inlet and outlet openings for the fibre material, a driveable rotor with a conical outer surface and a stator with a counter surface complementary to the rotor outer surface, with the rotor outer surface and the stator counter surface being at least predominantly occupied by milling tools to form a milling gap through which the fibre material flows and with both surfaces being adjustable relative to one another.
Pieces of apparatus of this kind, which are termed refiners, are known, and indeed with both milling gaps formed between conical surfaces and also with milling gaps formed between disc-like surfaces. An apparatus of this kind is, for example, described in DE 38 37 766 C2 which is incorporated herein by reference.
The so-called double disc and cone refiners are most frequently used for the milling of fibrous materials in the chemical pulp and paper industries.
With the increasing use of waste paper and short-fibre pulps, it is necessary to design comminution devices and refiners in such a way that a sensitive treatment of the fibrous materials is ensured, with the term sensitive treatment or caring milling being understood to mean a particularly pronounced preservation of the fibre length. As a rule milling machines with a larger number of knives bring about a more caring milling process.
In known cone refiners, the groove surfaces, i.e. the surfaces disposed between the knives, must normally be selected to be larger than in disc refiners because the centrifugal forces necessary to achieve the required hydraulic throughputs are smaller than in disc refiners. This leads to a reduction of the total knife length related to the conical surface and this can, in turn, lead to a corresponding reduction of the transmittable milling power. A disadvantage in the known cone refiners is furthermore that undesirably high axial forces act on the rotor bearing.